1. Field of the Invention
This application has relation to U.S. Pat. Nos. 5,191,815, 5,203,235, 5,233,889, 5,305,665 and 5,249,483.
The present invention relates in general to automatic transmissions of motor vehicles, and more particularly, a method and a device for controlling a hydraulically operated clutch of the automatic transmissions.
2. Description of the Prior Art
In order to clarify the task of the present invention, one device for electronically controlling the clutch of the automatic transmissions will be described, which is disclosed in European Patent Application No. 0339663A1.
In the disclosed device, for effecting 4.fwdarw.3 shifting, a clutch is subjected to a change from OFF (viz., disengaged) condition to ON (viz., engaged) condition, and at the same time, a brake is subjected to a change from ON (viz., engaged) condition to OFF (viz., disengaged) condition. The engagement of the clutch and disengagement of the brake are carried out in a given timing. That is, if the disengagement of the brake is carried out much earlier than the engagement of the clutch, the transmission is forced to have a relatively long neutral condition which causes undesired racing of the engine, and if the engagement of the clutch is carried out much earlier than the disengagement of the brake, the transmission is forced to have, for a relatively long time, an interlocked condition wherein both the clutch and the brake keep their engaged conditions which causes a marked shift shock.
In view of these facts, the above-mentioned European Patent application proposes a measure in which the hydraulic pressure of the clutch at the time of the 4.fwdarw.3 shifting is controlled. That is, a feedback control is effected to control the acceleration of an input rotation to a desired level. This feedback control deals with a certain time lag which would occur between the time when a control unit issues an instruction signal for engaging the clutch and the time when the clutch actually starts the engaging movement thereof. In fact, the delayed movement of the clutch is caused by the time lag between the time when, upon issuance of the instruction signal, feeding of hydraulic pressure to the oil chamber of the clutch starts and the time when, due to the increased pressure in the oil chamber, the piston of the clutch actually presses the drive and driven clutch plates to effect the engagement therebetween. In the disclosed measure, taking account of the inevitable delayed movement of the clutch, the instruction signal for the clutch engagement is issued earlier by a degree corresponding to the delayed time. Furthermore, in view of unavoidable dispersion of the delayed time in each friction unit of the transmission and unavoidable fluctuation of the delayed time in accordance with the operation condition of the transmission, correction is constantly made to the delayed time by using a learning control.
However, due to its inherent arrangement as described hereinabove, the disclosed device is compelled to have a complicated operation program for the electronic control unit, which causes complicated and expensive construction of the device and thus that of the transmission.